Download the TIWdteMental plugin and my modified mi file with node ids, melscripts and icons here.
And the DarkTree demo here. More shaders are availible here.
Download the cellular texture component addon here.How to use them in Maya.

Color and displacement shader.
Old clayroof with lichen
and dirt gathered in the crevices.

Color and displacement shader.
Old clayroof with dirt
gathered in the crevices.